1. Field of the Invention
The present invention relates to the use of polyurea compositions derived from polyphenyl polymethylene polyisocyanate and a select group of amines as adhesives.
2. Brief Description of the Prior Art
Non-sagging compositions are widely known and used commercially. Such materials are important because they are very convenient to use in many applications. An example would be adhesives and sealants used in automotive manufacturing where such formulations can be supplied and conveniently manipulated in a low-viscosity liquid form but then applied even to vertical surfaces as a thick non-running material.
Polyureas are also generally known in the art. Compared to polyurethane analogs, polyureas can have superior physical properties such as high temperature performance, adhesion, oil and solvent resistance, and tear strength. Due to the very high reactivity of most amine compounds toward isocyanates, polyurea formulations often have short gel-times, resulting in short "pot-life" (or working time). Therefore, polyurea compositions have been limited to applications where very short gel-times are desirable, such as in reaction injection molding. In addition, because only a few fast-reacting high-molecular weight polyamines have been available, the reactivity and viscosity profiles of polyurea formulations could not be adjusted sufficiently to provide non-sagging systems. Thus, although polyamines are known to impart sag resistance to polyurethane adhesive formulations (e.g., U.S. Pat. Nos. 4,444,976, 4,994,540, 5,128,433, 5,143,996, and 5,175,228), non-sagging adhesives containing only urea groups have not previously been described.
U.S. Pat. No. 5,128,433 discloses thixotropic polymer compositions comprising the reaction product of aromatic polyisocyanates, such as low molecular weight polyisocyanates based on 4,4'-diisocyanato-diphenylmethane, toluene diisocyanate or the like or their prepolymers, and one or more aromatic diamines. The compositions are said to be useful in making coatings, sealants, adhesive bonds and molds.
U.S. Pat. No. 4,954,199 discloses a structural member comprising a laminate and an adhesive where said adhesive is the reaction product of a specified proportion of polyurethane-urea forming components: (a) 100 parts by weight of at least one hydroxyl functional material having a molecular weight of at least 300 and a hydroxyl functionality of at least 2, said material being preferably selected from the group consisting of polyether polyols, polyester polyols, polyester amide polyols, and polycarbonate polyols; (b) 0.2 to 20 parts by weight of an aliphatic, aromatic, and/or a cycloaliphatic diamine or triamine; and (c) an organic isocyanate in an amount sufficient to render the isocyanate index between about 70 and about 150, wherein said component (c) is not prereacted with any of the components (a) and (b).
U.S. Pat. Nos. 5,164,473 and 5,204,439 disclose low viscosity two-component filled polyurethane adhesives which are useful as structural adhesives comprising a low viscosity isocyanate component in a quantity sufficient to provide an isocyanate index of about 100 to 150 comprising an organic polyisocyanate wherein up to 10 equivalent percent of the isocyanate groups of said polyisocyanate have been modified by reaction with one or more isocyanate-reactive compounds; a low viscosity curative component comprising 5 to 50 equivalent percent of a polyether polyol and/or a polyether terminated by aromatic amino groups having an equivalent weight greater than 500 based on the total equivalents of amino and hydroxyl groups of the curative component; 50 to 95 equivalent percent of one or more chain extenders comprising from 50 to 100 percent of the isocyanate-reactive equivalents based on the total equivalents of amino and hydroxyl groups of the equivalent component; and one or more isocyanate-reactive diamines or triamines in a quantity sufficient to produce adequate resistance to flow when the isocyanate and curative components are mixed, wherein at least one of these components contains at least one filler in a total quantity of from about 10 to about 40 percent by weight of the filled polyurethane adhesive.
During automobile manufacturing, structural adhesives that are used to bond polymeric automobile panels such as fascia can be subjected to temperatures of about 200.degree. C. or higher. At these high temperatures, many of the art-related adhesives such as polyurethane adhesives loose their integrity by foaming, cracking, and/or softening with a consequential loss in physical and other adhesive properties.
As would be realized, there is a need for structural adhesives that can withstand high temperatures.
Surprisingly, it was found that by using aminocrotonated polyethers, it is now possible to prepare blends containing only polyamine chain extenders and amine-terminated, soft-segment compounds with a balanced reactivity of the amines toward isocyanates. It is, therefore, possible in practice to prepare non-sagging all-urea compositions. Thus, the desirable physical properties of polyureas can now be combined with non-sagging characteristics. As would be realized, preparation of such compositions demands highly controllable reactivity in order to optimize viscosity profile, homogeneity, gel-time, working life, and green strength. An unbalanced reactivity of the amines can also result in agglomeration of urea upon mixing with the isocyanate. This leads to inhomogeneous materials and unacceptable physical properties. By the present invention, one avoids the above problems because it is now possible to prepare all-amine blends of chain extenders and soft segments which provide improved reactivities and physical properties.